Delivery of an exogenous gene to a cell, and expressing the gene once it is delivered, is more difficult in some cell types than others. While numerous processes of enhancing exogenous gene delivery and gene expression have been developed, there is a continuing need for improved methods.
While gene transfer to cells and tissues is often complex, it is particularly difficult to transfer exogenous genes into epithelial cells (1-8). It is believed that this resistance reflects the barrier function of these tissues and failure of epithelial cell apical membranes to uptake gene transfer vectors such as adenoviral particles (4, 5). In contrast to lack of endocytic activity of epithelial apical membranes, basal membranes of epithelial cells do allow endocytosis. However, basal membranes are not accessible because of the tight junctions between cells.
Difficulty with gene transfer in epithelia using adenovirus vectors is well documented (4-6). However, such problems are not limited to adenoviral constructs and it is reasonable to imagine that the barrier function of epithelia may substantially limit transduction efficiency with vectors unrelated to adenovirus by a similar mechanism.
A number of methods have been used, both in vitro and in vivo, to overcome cellular resistance to introduction of exogenous genes. While EDTA, EGTA, other calcium chelators, and abrasion all augment gene transfer to epithelial cells, results are still less than optimal for effective in vitro studies as well as for gene therapy applications (7-8).
Gene therapy is the treatment of a pathological condition by introduction of an exogenous gene into a cell or tissue. In inherited diseases such as sickle cell anemia, α1 antitrypsin deficiency, phenylketonuria, hemophilia and cystic fibrosis, the goal of gene therapy is to replace a missing or defective gene in order to allow a cell or tissue to function normally. Gene therapy can also be used to eliminate abnormal cells. In pathological conditions such as cancer, inflammation and autoimmunity, this technique allows for introduction of toxins which cause death of the targeted abnormal cells.
In spite of the promise of gene therapy for management of intractable disease, inefficient transfer of genes into cells has slowed progress towards the goal of routine, reproducible treatment. The refractoriness of cells and tissues in vivo is well known. The required level of gene transfer is rarely attained in current gene therapy protocols even though only a small number of cells are required to express the therapeutic gene in order to ameliorate the pathological condition (1-3). For instance, for treatment of cystic fibrosis it has been suggested that if 5% of target epithelial cells express one Cystic Fibrosis Transmembrane Conductive Regulator (CFTR) mRNA molecule per cell, the physiologic C1− transport defect in the airways may be overcome. Nevertheless, it has not been possible to consistently achieve even this low level of gene transfer in vivo using conventional adenoviral or other vectors.
The discovery of new means of facilitating gene transfer and enhancing exogenous gene expression would benefit both clinicians and bench scientists. Thus, if a safe transient activator of gene transfer or expression to otherwise refractory cells, tumors or tissues were identified, this agent could be administered in combination with a vector encoding a gene of choice.